I've been looking into purchasing a .223 bolt action and I would love recommendations. More importantly, I want to hear opinions on using 5.56x45 NATO rounds in a rifle chambered for .223. I've seen comments all over the Internet stating either that firing the 5.56 from a .223 rifle will be completely fine, or that it will likely lead to catastrophic failure. What do you guys think?

That's what the manufacturer claims, but there's also a lot of folks who claim that they've loaded 5.56 into a rifle chambered for .223. They claim that even though the .223 is a civilian caliber and that it is rated for a lower pressure, the 5.56 shouldn't cause catastrophic failure (aka explosion). Is there anyone out there who have actually tried it out?

It is officially unsafe as per SAAMI to run 5.56 in a .223 chamber. The 5.56 runs a substantially higher pressure in a .223 chamber than it would in a 5.56 chamber because of how the round fits into the barrel when it is chambered. The 5.56 chamber has a bit more play, thus it doesn't have pressure spikes. It's sort of becuase the round will initially be "stuck" and pressure rapidly builds behind it. Just don't do it. The only reason some people can get away with it is becuase their rifle is out of spec slightly. Just get a 5.56 I'd say, although becuase the chamber is "looser" it will be slightly less accurate when firing .223 from the 5.56 - but it's such a small difference you're average guy at the range wouldn't notice.

Long answer: A 5.56 would fire in a 223 gun but each time you do its stressing the chamber beyond its rated pressure. You may be able to fire 5.56 out of a 223 50,100, 200 times with no issue but you are introducing micro fractures into the metal each time the chamber exceeds its rated pressure. It would wear the chamber down until one day it goes KABOOM!

Another issue is that the 5.56 spec calls for the chamber throat to be slightly longer than a 223 spec chamber throat. 223 rifle chambers are usually manufactured with tight tolerances to improve accuracy. If you load a 5.56 into a 223 chamber that has tight tolerances you could be deforming the case neck or causing bullet set back. Both of which would lead to a over pressure in the cartridge and a potential explosion. Since the 5.56 spec chamber throat is longer, you can safely use 223 in a 5.56 chamber. You just lose accuracy because the cartridge isn't seated up against the barrel throat as it is when using 5.56 in a 5.56 chamber.

The problem you run into is that mil spec 5.56 is made by damned near every ammo plant in the world. You run into a lot of variation in case/neck thickness, case length, and OAL, not to mention powders and primers. Every one of those parameters effects case pressure.

A 5.56 chamber is more forgiving vs a strict .223 reamed chamber. The one time where you do want an actual .223 chamber is if you are going to be using your rifle for target/accuracy shooting, and you will only shoot actual .223 cartridges.

__________________
"Oil leak, what oil leak? That puddle under the car is just sweat from all that horsepower."